1. Technical Field
The present invention relates to a lighting control circuit for vehicle lighting equipment and, more particularly, a lighting control circuit for vehicle lighting equipment constructed to control the lighting of a semiconductor light source that is formed of a semiconductor light emitting device.
2. Related Art
In the prior art, as the vehicle lighting equipment, the equipment using a semiconductor light emitting device such as LED (Light Emitting Diode), or the like as a light source is known. Also, the vehicle lighting equipment of this type is equipped with a lighting control circuit that controls the lighting of the LED. In constructing the headlamp using the LED as a light source, as modes of a combination of the LED and the lighting control circuit for the vehicle lighting equipment (power supply circuit) to control the lighting of the LED, the mode (one line drive) in which the lighting control circuit for the vehicle lighting equipment (power supply circuit) is connected across a plurality of series-connected LEDs and then the same current is supplied to all LEDs from one lighting control circuit for the vehicle lighting equipment (power supply circuit), the mode in which the unit for turning on one LED or a plurality of series-connected LEDs by one lighting control circuit for the vehicle lighting equipment is provided in plural, and others may be applied.
In case the headlamp is constructed in accordance with any one of the above modes, the LED(s) must be packaged onto the substrate, or the like. However, when the worker's hand, etc. are charged with static electricity upon packaging the LED(s) onto the substrate, or the like, in some cases an overvoltage generated due to the static electricity is applied to the LED(s) to bring about the breakdown of LED.
Therefore, in order to protect the LED from the static electricity, it was proposed to connect the capacitor, the resistor, and the Zener diode in parallel with the LED (see JP-A-11-331494 (page 3 to page 4, FIG. 1)).
Meanwhile, after the headlamp using a plurality of LEDs as a light source is constructed by packaging a plurality of LEDs onto the substrate, or the like, the luminous intensity distribution characteristics of the headlamp is changed when a part of LEDs is broken down. Therefore, a function of informing the driver of the effect that the LED is broken down when any one of LEDs is broken down must be added. In other words, in the case where the headlamp is constructed by a plurality of LEDs, when only a part of the LEDs is broken down and the remaining LEDs are still turned on, it is difficult for the driver to know that a part of LEDs is broken down, based on a change of the luminous intensity distribution characteristics of the headlamp.
In sensing the breakdown of LED, normally the current is not supplied to the LED at all when the wiring of the LED is disconnected, for example. Therefore, if a current sensor for sensing that the current is reduced or the current becomes zero is provided and then an indicator lamp is turned on based on a sensed output of this sensor, the indicator lamp can inform the driver of the fact that the LED is broken down.